In a color projection display the light from the lamp is divided into red, green and blue color channels, then modulated in each channel independently and finally recombined in one image on the screen. In other words, color maintenance in projection display consists of two steps: color splitting and color recombination. The color channels can be spatially separate (e.g., a three-panel display) or separated in time (e.g., a single-panel display).
Color splitting must provide the required (desired) color purity in each channel, which can be quantified with the color coordinates described in E. Stupp and M. Brennesholtz, “Projection Displays,” Wiley, 1999, p. 310–312. Color recombination from all three channels must give the required (desired) white color, which also can be described with color coordinates or color temperature. One common color standard is set forth in Society of Motion Picture and Television Engineers: Recommended Practice, RP 145-1999 entitled “SMPTE C Color Monitor Colorimetry.”